1. Field of the Invention
The present invention relates in general to apparatus for determining flow-related information in a well-bore and more particularly to apparatus for injecting radioactive material in the area of the well-bore which is under investigation.
2. Description of the Prior Art
With the present world oil situation, there is greater emphasis upon increasing domestic oil supplies which has resulted in increased activity in drilling new wells and also in bringing old wells back on-line which had previously been shut down. It is well known in the art of drilling new wells and/or re-opening old wells to perform well logging functions to determine desired information related to the well and the surrounding formations. The well loggers lower devices called logging tools into the well-bore on wireline. Such tools usually depend upon the force of gravity to permit positioning of the well tool at the desired location within the well-bore. There are many types of logs which are run, one of which is radioactivity logs. In the procedure to obtain the radioactivity logs, radioactive material is injected into the well-bore area which is under investigation and the radioactive material is then detected or traced with detection equipment which is located a known distance from the point of injection of the radioactive material. In order to obtain the most accurate results from the logs, the amount of radioactive material injected into the well bore area must be accurately known. These radioactivity logs are used to provide log injection profiles; determine zones of lost circulation and channel problems; locate cement tops in cementing casing; identify water and oil entry areas in producing wells; etc.
In the prior art injector tools, an electrical feed-thru is provided which allows the tool to be used anywhere in a string of production logging tools. A D-C motor is positioned within the tool and is operatively coupled to a ball-screw drive. The ball-screw drive is coupled through a piston rod to a piston, whose travel within a reservoir, whose walls are formed by the tool housing, causes the liquid radioactive material to be ejected therefrom through an orifice in the side of the reservoir. With a given size of piston bore, the length of travel of the piston determines the amount of radioactive material which is injected into the well-bore. Of course, the amount of travel of the piston is determined by the amount of rotation of the motor and the resulting travel of the ball-screw. The prior art injector tools are plagued by motor and ball-screw problems. Any attempt to operate the injector tool in an environment above about 145 degrees C. causes an increase in the motor problems, while severe derating of the motors then leads to space problems on all diameters. The loading and reloading of the tool, wherein a funnel is used to introduce the radioactive material into the reservoir, can be messy and lead to radioactive contamination of personnel and facilities. In the overall operation of the prior art injector tools, lack of consistent and accurate tracer shots is a problem.
The invention as claimed is intended to provide a remedy for inaccurate and inconsistent tracer shots. It also provides an injector apparatus with a temperature rating of up to 200 degrees C. with reliable and accurate operation. The possibility of spillage of the radioactive material by the operator is virtually eliminated. In addition, the invention allows the injector portion of the logging tool to be smaller in diameter and length.